1. Field of the Invention
The present invention relates to a radar module and an antenna device for an FM millimeter-wave radar alarm system for use on motor vehicles.
2. Description of the Prior Art
One known motor vehicle radar alarm system has an electronically scanning planar antenna array as disclosed in U.S. Pat. No. 5,008,678. The disclosed electronically scanning planar antenna array comprises a plurality of transmitting and receiving planar antenna elements, a pair of passive phased arrays such as planar microstrip Butler matrixes, and a pair of electronic switches which are combined to transmit and receive a scanning beam.
The conventional electronically scanning planar antenna array is disadvantageous in that the passive phased arrays thereof cannot scan a relatively large angular range with the scanning beam. Another problem is that the planar antenna array requires both a transmitting array of antenna elements dedicated to transmitting radar signals and a receiving array of antenna elements dedicated to receiving echo signals. This imposes limitations on conventional systems which make it difficult to reduce the size of the planar antenna arrays used therein and, especially difficult to install such planar antenna arrays on motor vehicles.
German laid-open publication No. 4307009 discloses an antenna device for a radar module.
IEEE TRANSACTIONS ON MICROWAVE THEORY AND TECHNIQUES, VOL. MTT-26, NO. 1, January 1978, shows an MIC Doppler module with output radiation normal to the substrate plane.
Japanese patent publication No. 57-24968 discloses a microwave IC case.
Japanese laid-open utility model publication No. 1-126714 discloses an antenna device.